An all-new, fourth-generation Prius debuted in 2016. As with the previous generation, its Hybrid Synergy Drive combines the output of a 1.8-litre four-cylinder gasoline engine and two motor/generators through an electronically controlled planetary-type continuously variable transmission. The newest Prius uses smaller, lighter hybrid components, including a lithium-ion hybrid battery in addition to the existing nickel-metal hydride. A smaller transaxle and power control unit allow for the auxiliary battery to be installed in the engine compartment. New shift-by-wire technology uses electric signals to transmit shift operations. For 2017, the Prius is offered in a single model with four trim levels — Prius (with Upgrade Package), Touring, Technology and Technology with Advanced Package. New for 2017, every Prius now includes Toyota Safety Sense P as standard, featuring the Pre-Collision System, lane departure alert, automatic high beam and dynamic radar cruise control. All 2017 models are also now equipped with standard heated front seats.